For the pendant lights, it's not mounted to the plaster ceiling itself as it will not hold over time. Usually the electrician will bolt it to a timber support (some sites refer to it as lath, can't for the life of me remember what its called locally) within the plaster ceiling.

Same would apply for track lights, better to install it to something with better support to avoid cracks on your plaster ceiling due to the weight of the light fixture.

The metal pieces holding your plaster ceiling are not strong enough to hold your light fixtures. You would also want to avoid installing on those simply because any electricity leak would turn the metal pieces into conduits and potentially cause more problems.

You can try drilling first to see if there is anything to bolt the fixtures too, but to properly do the installation you'd need to cut a hole in the plaster ceiling. Putting back the cut out piece is not too difficult or messy if done right and most electrician's would be familiar with the process. Just be prepared to repaint and touch up the plaster ceiling on completion.